Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$37.54	7.431%	$40.3296	$40.33	$40.35	$40.30
Purchase #2	$28.89	11.566%	$32.2314	$32.23	$32.25	$32.20
Purchase #3	$93.97	5.165%	$98.8236	$98.82	$98.80	$98.80
Purchase #4	$215.99	6.496%	$230.0207	$230.02	$230.00	$230.00
Purchase #5	$36.54	9.672%	$40.0741	$40.07	$40.05	$40.10
Purchase #6	$40.32	12.299%	$45.279	$45.28	$45.30	$45.30
Purchase #7	$96.53	6.173%	$102.4888	$102.49	$102.50	$102.50
7 purchase totals =	$549.78		$589.2472	$589.24	$589.25	$589.20